The Developer profile grants you some privileges on your QlikSense applications.
Duplicating app
When your app is published you will be able to see it in the corresponding stream.
If you are owner of the app (If you publish it), you can duplicate it by right click.
When the app is duplicated, a copy of the published app appears in the My work stream.
By this way you can modify it without modify the published app.
Publishing and replace your app
When you're ready to publish a new version of the app, you can do it by right cliking on the duplicate app in My work.
Note : If you publish for the first time please go to this section : Publish your app at the first time
If the app is a duplicate of the published app, you will be able to publish and replace the existing app.
Warning : If you duplicate a duplicated app, you won't be able to publish and replace the existing app.